Lucent Technologies Victory Class Batteries WP-93936
Issue 1 May 2000
Installation 6 - 13
Cell Installation Guidelines, continued
Measuring Specific
Gravity of a Cell
Using a Hydrometer
A hydrometer float inserted in a glass-barreled, rubber bulb syringe is
used to measure the specific gravity of electrolyte. The float is
graduated in points of specific gravity, wherein 0.001 equals one point
of specific gravity. The specific gravity is read on the hydrometer scale
at the level at which it floats in the electrolyte.
Note: Digital electronic hydrometers are available and may provide a
more convenient method of measurement for your needs. They still
require immersion into the electrolyte, and the same care should be
taken to avoid spillage of electrolyte onto the cell and connections.
Specific gravity readings are taken through the vent funnel. When
taking hydrometer readings, always hold the hydrometer syringe
vertically and make sure the float is floating freely with no pressure
applied to the bulb. The glass parts of the hydrometer syringe should be
washed with soap and warm water as needed and rinsed with clear
water to keep them clean and accurate.
The specific gravity of a fully charged Victory Class cell is 1.215 at
77°F (25°C). As the cell discharges, the hydrometer will measure a
lower specific gravity. A hydrometer reading is, therefore, an indication
of the state of charge or discharge of the cell. However, note that
readings on recharge lag behind the ampere-hours returned on charge.
The specific gravity does not immediately indicate the true state of
recharge. Mixing the electrolyte is dependent upon the amount of gas
generated and acid diffusion. Usually, specific gravity measured at the
top of the cell is only accurate following an equalizing charge during
which the cell has gassed enough to thoroughly mix the electrolyte.
This is because concentrated acid formed at the plates during charge
drops to the bottom of the cell container because it is heavier than the
depleted electrolyte solution.
Specific gravity readings should be taken when the battery is first
installed. Additional readings should not be necessary unless visual
inspection reveals signs of crystallization.
